Central heating and/or cooling systems typically employ a central fluid heating and/or cooling plant and respective conduits for directing the heated or cooled fluid to the rooms, offices, etc., in the house, unit or building being serviced by the system. A zone control apparatus for such systems may be employed to eliminate unnecessary heating/cooling of individual rooms or zones consisting of one or more rooms during cyclical periods of low or no use. Zone control apparatus are disclosed in U.S. Pat. No. 4,545,524 issued on Oct. 8, 1985 and entitled "Zone Control Apparatus for Central Heating and/or Cooling Systems"; U.S. Pat. No. 4,600,144 of the same title and issued on Jul. 15, 1986; and U.S. Pat. No. 4,702,412 of the same title and issued on Oct. 27, 1987.
The zone control apparatus disclosed in the above mentioned patents are characterized by one or more flow control devices which are installed in respective fluid conduits of the central heating and/or cooling system, and a cycle controller for cycling the flow control devices between high and low (or no) flow conditions. When in their low flow condition, the flow control devices restrict and preferably close off fluid flow through the associated conduits to minimize or eliminate direct heating or cooling of the associated rooms. The flow control devices are preferably located remote from the terminating ends of the fluid conduits to minimize heating or cooling losses associated with long conduits.
In certain systems, such as forced air systems, control of fluid (air) flow may be obtained by a bladder located interiorly of the fluid conduit. The bladder may have an air inlet fitting which may be used to anchor the bladder in place. The air inlet fitting may be coupled to an air supply line which may be selectively connected to a source of pressurized air, such as an air pump, and to the atmosphere respectively to inflate and deflate the bladder.
Desirably, the bladder when deflated should allow substantially unrestricted flow of the fluid through the conduit. On the other hand, the bladder when inflated should substantially if not totally restrict fluid flow through the conduit. Additionally, the bladder should be able to withstand and undergo an indefinite number of inflation cycles. This criteria should be met for conduits of varying sizes and shapes including HVAC ducts which typically are circular or rectangular.